1. Field of the Invention
The present invention relates to mobile communication systems and, in particular, to an access admission control method and system for determining access to a SAE/LTE (System Architecture Evolution/Long Term Evolution) system.
2. Description of the Related Art
In a conventional Wideband Code Division Multiple Access (WCDMA) mobile communication system, a node B refers to a network component operating as a base station for securing the coverage of an operator's network. Recently, Node B base stations have been installed to cover a shadow area or at the customer premise to allow access to a 3rd Generation (3G) core network via a public Internet Protocol (IP) network, e.g., Ethernet and Asymmetric Digital Subscriber Line (ADSL). Such a base station is referred to as a “femto base station,” and the cell served by the femto base station is referred to as a femto cell. Particularly, the in-home evolved Node B base station is referred to as a Home Node B (HNB) in the WCDMA system. Unlike the conventional Node B, the HNB is able to allow access of only the user equipment (UE) registered for the HNB utilization. This is called “admission control.”
FIG. 1 is a sequence diagram illustrating operations when an UE attempts to access the HNB.
Referring to FIG. 1, the HNB/HGW (HNB Gateway) 102 acquires the UE identification information, i.e. International Mobile Subscriber Identity (IMSI) through OA&M (Operations, Administration, and Maintenance) processes (104). OA&M processes are well-known in the art and need to be described in detail herein.
The UE 100 sends the HNB/HGW 102 a Non Access Stratum (NAS) Request message containing its IMSI to request access to the HNB (106). The NAS can be a messaging protocol used for signaling and traffic between the UE and a Core Network (CN) in the Universal Mobile Telecommunications System (UMTS), e.g. Attach or Routing.
Upon receipt of the NAS request message containing the IMSI of the UE, the HNB/HGW 102 checks whether the IMSI exists in an IMSI list (108). If the IMSI exists in the IMSI list, i.e. the UE 100 is allowed access to the HNB. The HNB/HGW 102 sends the UE 100 a NAS Accept message (110) in response to the NAS Request message (106), whereby the UE accesses the HNB successfully for the next operation. Otherwise, if the IMSI of the UE 100 does not exist in the IMSI list, i.e. if the UE 100 is rejected from accessing the HNB, the HNB/HGW 108 sends the UE 100 a NAS Reject message (112).
As described above, the HNB/HGW (102), whether physically independent or combined, performs the admission control process based on the IMSI in the conventional WCDMA system such that the either the HNB or the HGW must have the IMSI information to determine whether to accept or reject the UE from accessing the network. That is, the operator inserts the IMSI information of allowed UEs into either the HNB or the HGW (or both) manually. However, storing the security-sensitive IMSI information of the subscriber within an entity located on the public IP network is prone to cause security problems, and frequent update of the IMSI list increases maintenance cost.